✔ 最佳答案
f(x) = 2x²-5x+2
f(4) = 2×4² - 5×4 + 2
= 32 - 20 + 2
= 14
f(4+h)
= 2(4+h)² - 5(4+h) + 2
= 2(16+8h+h²) - 20 - 5h + 2
= 32+16h+2h²-20-5h+2
= 2h²+11h+14
(f(4+h)-f(4))/h
= 2h+11
As h→0
(f(4+h)-f(4))/h → 11
If you are familiar with derivatives note that f'(4)=11